Fuel system having variable displacement pump failure modes

Abstract

A fuel system can include a main fuel pump (MFP) configured to output main flow to a main line, an augmentor fuel pump (AFP) configured to output an augmenter flow to an augmenter line, and a variable displacement pump assembly (VDPP) in fluid communication with the AFP via the augmentor line to receive the augmentor flow. The VDPP can include a variable displacement pump (VDP) configured to output a VDP flow to a VDP output line. The system can include a main fuel throttle valve assembly (MFTV) in fluid communication with the main fuel pump via the main line to receive the main flow and in fluid communication with the VDPP via a backup line. The MFTV can be in fluid communication with an engine line, an actuation assembly in fluid communication with the VDPP via an actuation line to receive an actuation flow.

What is claimed is: 
     
       1. A fuel system, comprising:
 a main fuel pump (MFP) configured to output main flow to a main line; 
 an augmentor fuel pump (AFP) configured to output an augmenter flow to an augmenter line; 
 a variable displacement pump assembly (VDPP) in fluid communication with the AFP via the augmentor line to receive the augmentor flow, wherein the VDPP includes a variable displacement pump (VDP) configured to output a VDP flow to a VDP output line; 
 a main fuel throttle valve assembly (MFTV) in fluid communication with the main fuel pump via the main line to receive the main flow and in fluid communication with the VDPP via a backup line, wherein the MFTV is in fluid communication with an engine line, 
 an actuation assembly in fluid communication with the VDPP via an actuation line to receive an actuation flow; 
 wherein in a start mode, the VDPP is configured to output the VDP flow to the actuation line and the backup line, and wherein the MFTV is configured to output the VDP flow to the engine line, 
 wherein in a run mode, the VDPP is configured to output the VDP flow to the actuation line and the backup line, and wherein the MFTV is configured to output the main flow to the engine line, 
 wherein in an initial VDP failure mode, the MFTV is configured to output the main flow to the backup line to provide the VDPP with the main flow as well as provide main flow to the engine line, and wherein the VDPP is configured to output the main flow to the actuation line to provide the main flow to the actuation assembly, and 
 wherein in a VDP failure mode, the MFTV is configured to output the main flow to the backup line to provide the VDPP with the main flow as well as provide main flow to the engine line, and wherein the VDPP is configured to output the augmentor flow to the actuation line to provide the augmentor flow to the actuation assembly, wherein the VDPP includes one or more valves configured to enable to the start mode, the run mode, the initial VDP failure mode, and the VDP failure mode, wherein the one or more valves includes an actuation selector valve (ASV) in fluid communication with the AFP and the VDP, wherein the ASV is configured to select between the VDP output line and the augmentor line to fluidly communicate with an ASV output line and the actuation line, wherein the one or more valves includes a backup selector valve (GGSV) connected between the ASV output line and the backup line. 
 
     
     
       2. The system of  claim 1 , further comprising an augmentor fuel control in fluid communication with the MFTV via an augmentor fuel control line and configured to receive an augmentor fuel control flow from the MFTV. 
     
     
       3. The system of  claim 2 , wherein the MFTV includes a regulator connected between the backup line and the augmentor fuel control line such that the regulator receives flow from the backup line and outputs the augmentor fuel control flow. 
     
     
       4. The system of  claim 3 , wherein the MFTV includes an MFTV check valve (CV) disposed between the main line and the backup line, wherein the MFTV CV is configured to open in the initial VDP failure mode to fluidly communicate the main line with the backup line to provide main flow to the VDPP. 
     
     
       5. The system of  claim 4 , wherein the MFTV includes a selector valve (SV) connected between the backup line, the main line, and the engine line, wherein the SV is configured to select between the main line and the backup line to fluidly communicate with the engine line. 
     
     
       6. The system of  claim 5 , wherein in the start-up mode, the SV is configured to select the backup line to fluidly communicate with the engine line, wherein in all other modes, the SV is configured to select the main line to fluidly communicate with the engine line. 
     
     
       7. The system of  claim 1 , wherein in the startup mode, the run mode, and the initial VDP failure mode, the ASV is configured to be in a first position to select the VDP output line to fluidly communicate with the ASV output line and the actuation line to provide VDP flow to the ASV output line and the actuation line, and the GGSV is configured to be in an open position to fluidly communicate the ASV output line and the backup line to provide VDP flow to the backup line. 
     
     
       8. The system of  claim 7 , wherein in the VDP failure mode, the ASV is configured to be in a second position to select the augmentor line to be in fluid communication with the ASV output line and the actuation line to provide augmentor flow to the ASV output line and the actuation line, and the GGSV is configured to be in a closed position to prevent fluid communication of the ASV output line and the backup line. 
     
     
       9. The system of  claim 8 , wherein the ASV and the GGSV are pressure controlled. 
     
     
       10. The system of  claim 9 , wherein the VDPP includes a solenoid in fluid communication with the augmentor line and an input line to output a solenoid control pressure to each of the ASV and the GGSV. 
     
     
       11. The system of  claim 10 , wherein the ASV is biased to the second position and includes a first ASV control port connected to the input line and a second ASV control port connected to the solenoid to receive the solenoid control pressure. 
     
     
       12. The system of  claim 11 , wherein the GGSV is biased to the closed position and includes a first GGSV port in fluid communication with the input line, and a second GGSV port in fluid communication with the solenoid to receive the solenoid control pressure. 
     
     
       13. The system of  claim 12 , wherein the VDPP includes a VDP check valve (CV) configured to prevent backflow to the VDP. 
     
     
       14. The system of  claim 13 , wherein the MFP includes one or more centrifugal pumps. 
     
     
       15. The system of  claim 1 , further comprising a boost pump connected configured to provide boost pressure to an input line. 
     
     
       16. The system of  claim 1 , further comprising a heat exchanger on the main line. 
     
     
       17. The system of  claim 1 , wherein the MFP includes a thermal recirculation line in fluid communication with the main line.